newborn vs immature

newborn is a noun but immature is not a noun.

Word	Noun	Adjective	Verb	Adverb
newborn	Yes	Yes	No	No
immature	No	Yes	No	No

newborn (noun)	immature (noun)
a baby from birth to four weeks

newborn (adjective)	immature (adjective)
having just or recently arisen or come into existence	not yet mature
recently born	characteristic of a lack of maturity
	(used of living things especially persons) in an early period of life or development or growth
	(of birds) not yet having developed feathers
	not fully developed or mature; not ripe